From what I have read about railways during the years of the Second World War there was no additional security against 'terrorist' type incidents apart from the generally heightened vigilance common during those years. Danger came from the skies, not from one's fellow citizens.
There was indeed fear of spies and posters were put up proclaiming
"Careless talk costs lives" and "Be like dad and keep mum"
I've mentioned this before, but one "security" ploy during WW2 was to remove road and other signs in order to confuse any German spies or troops parachuted into England. Reading was thought to be high risk and destinations were altered on its trolleybuses to confuse any invaders such as Tilehurst was shown as "The Bear Inn"
Members of the Light Railway Transport League once went to record the final years of the Southampton tram system during the war and were met by a posse of police on returning to London (by train, of course, as few people in those days had a car) having been reported as photographing certain locations which were forbidden